The present invention relates generally to rotor-type carburetors utilized in internal combustion engines, and more particularly provides an improved turbine rotor assembly for use in this type of carburetor, and associated construction methods for the improved rotor assembly.
The rotor-type carburetor, also referred to as a "central injection device", has been proposed, in various versions thereof, as a replacement for the conventional carburetor in a variety of internal combustion spark ignition engines because of its very advantageous provision of an essentially constant fuel-air ratio (.lambda.) over all operating speeds of the engine. Examples of these devices are disclosed in U.S. Pat. Nos. 3,991,144, 4,283,358, and 4,474,712. In its basic operating format, the rotor-type carburetor is provided with a bladed turbine rotor section which is coaxially and rotationally disposed in the air intake passage of the engine upstream of the butterfly damper therein. During operation of the engine, ambient air drawn inwardly through the engine's air intake passage causes rapid rotation of the bladed rotor section. A centrifugal pumping mechanism formed within the rotor draws fuel from a source thereof into the rotor and forces the received fuel outwardly through the rotor, via at least one lateral fuel discharge bore, onto and across a coaxially carried atomization ring into the ingested air stream. Importantly, the quantity of finely atomized fuel entering the air stream is in an essentially constant ratio to the ingested quantity of air, thereby essentially eliminating the fuel-air ratio variation problems commonly encountered in conventional carburetors.
While previously proposed rotor-type carburetors have proven to be quite effective in providing this very desirable constant fuel-air ratio benefit, it is now seen as desirable to improve various structural aspects of, and assembly techniques for, this type of carburetor. For example, the turbine rotor section of this type of carburetor has heretofore been relatively complex (and thereby relatively costly) to fabricate and assemble. This relative complexity and costliness of the turbine rotor section has previously arisen due primarily to the concomitant requirements that the rotor section be of at least relatively light-weight construction, have a high degree of dimensional precision (particularly with regard to the internal passageways defining the centrifugal pump portion of the rotor), and provide effective sealing between its various components, and particularly with respect to the seal between the stationery fuel line and the rotating rotor.
To meet these important design criteria, previously proposed turbine rotor structures have been of essentially all-metal construction (at least as to the central hub portion thereof) in which a relatively large number of metal parts must be precisely fabricated and accurately assembled. This results in relatively high mass, which causes lags in changing the rotational speed of the rotor in response to changes in the volumn of air flow.
Since, after the engine is turned off, this residual centrifugal pumping action is neither necessary nor particularly desirable, it can be seen that it would be advantageous to provide a mechanism for automatically decreasing the spin-down time of the turbine rotor section, to make changes in the speed of the rotor more closely follow changes in the volumn of air flow.
As mentioned above, the typical turbine rotor section has a laterally disposed internal orifice through which fuel is discharged for ultimate dispersal into the ingested air stream as a fine mist or "fog". Such orifice, of necessity, is disposed above the float-maintained fuel level in the engine's float reservoir. This height differential between the orifice and the maintained upper level of the fuel creates a siphon-breaking air gap upon engine shutdown to prevent outward siphoning of fuel through the orifice after the engine has been stopped. While this is, of course, a necessary and very desirable feature it also means that during engine startup fuel must be centrifugally pumped upwardly into this air gap to fill it, to provide the necessary fuel outflow through the orifice. This results in at least a slight delay between the initiation of turbine spin up and the required outflow of fuel through the orifice. It can thus be seen that it would be quite desirable to eliminate or at least substantially reduce this fuel delivery delay.
Several other problems or limitations have been commonly associated with the turbine rotor assemblies of the central injection carburation devices discussed above. For example, because it is desirable for the turbine section to operate with minimum friction, it has been desirable to provide a hydrostatic seal which operates without sliding contact with other structural members, the turbine spin-down time after air flow is stopped by throttle action is relatively long. Of course, during such spin-down condition, the centrifugal fuel-pumping action of the turbine rotor assembly, to at least a limited extent, is operative until the rotation of the turbine rotor ceases.
Finally, because of the relatively high number of parts required to fabricate previously proposed turbine rotor sections, a concomitantly high number of internal sealing mechanisms must also be provided to prevent undesired fuel flow past various interfacing portios of such parts. This heretofore unavoidable sealing complexity adds to the cost of fabricating and assembling the turbine rotor section, and also can potentially adversely affect its reliability and operating efficiency.
Accordingly, it is an object of the present invention to provide an improved turbine rotor structure, and associated assembly methods therefor, which eliminates or minimizes above-mentioned and other problems and limitations associated with previously proposed turbine rotor sections of rotor type carburetors.